DR CHARLES O. BABKLA ON POLARISED R6NTGEN RADIATION. 473 



By turning the bulb through a right angle the electroscope which had previously 

 indicated a maximum of intensity indicated a minimum, and vice verad. The position 

 of the bulb when the vertical secondary beam attained a maximum of intensity 

 and the horizontal secondary beam a minimum was that in which the kathode stream 

 was horizontal (see fig. 1), the maximum and minimum being reversed when the 

 kathode stream was vertical. By turning the bulb through another right angle, so 

 that the kathode stream was again horizontal but in the opposite direction to that in 

 the other horizontal position, the maximum and minimum were attained as before. 



These are the results that were expected from a consideration of the theory of the 

 production of X-rays. 



Many experiments were made in order, if possible, to account for these results in 

 any other way than on the theory of partial polarisation of the primary beam. 



By placing lead screens in front of apertures C, and C 7 , it was found that the 

 resulting deflexions of the electroscopes A, and A, were negligible in any position of 

 the bulb. They were therefore due to the radiations proceeding through these 

 apertures. No direct radiation passed through them, hence there were variations in 

 the intensity of secondary radiation with changes of position of the bulb. 



Placing radiators of the same material but of very different mass in the position 

 shown in the diagram showed that, though the absolute intensity of secondary 

 radiation was considerably altered, the relative changes produced by turning the 

 bulb were, within the limits of experimental error, unchanged. 



When different substances, which emitted a secondary radiation differing little from 

 the primary, were used as secondary radiators, variation in intensity was exhibited 

 to approximately the same extent. 



When all solid radiators were removed and only the secondary radiation from air 

 could affect the electroscopes, relative changes of the same order of magnitude were 

 observed. 



It was thus conclusively proved that the total intensity of secondary radiation in a 

 given direction depended on the position of a plane passing through the axis of the 

 primary beam and fixed in the beam. 



As the secondary radiators were not very small in area, we have to consider the 

 possibility of the primary radiation incident on the secondary radiator not being 

 uniform in intensity over the whole of the radiator and the effect of this. 



The angle subtended by extreme points of the radiator at the antikathode was 

 very small, being about 6, so that the variation in intensity through this angle could 

 only be small. But admitting the possibility of a distribution of the primary 

 radiation which was not uniform, there would be a corresponding distribution of the 

 intensity of secondary radiation, and the two secondary electroscopes not being 

 equidistant from all points of the radiator would be affected to a greater extent by 

 the nearer portions. I, however, find it impossible to conceive of any distribution of 

 intensity which would account for the results obtained. It was experimentally found 

 VOL. CCTV. A. 3 P 



